The ability of somatic mutation to modify the course of a humoral immune response is well documented. However, the focus has been almost exclusively on the ability of this process to improve the functional characteristics of representative antibodies; the harmful effects have not been well characterized. Yet in terms of cell numbers, all evidence suggests that B-cell wastage caused by harmful somatic mutations probably far exceeds the number of cells whose antibodies are improved through mutation. The purpose of this project is to gain quantitative insight into the contribution of mutation to B-cell wastage and secondly to exploit the well-known power of harmful mutations, to illuminate function. The investigators have previously made and characterized in vitro the binding of a large number of mutants of the T15 antibody to the hapten, phosphocholine (PC). The hypothesis is that mutant Abs displaying defective Ag binding or secretion in vitro would lead to apoptosis and B-cell wastage if they were to occur in vivo. This hypothesis will be tested in three ways: 1) by examining the ability of mutant antibodies to recognize PC which is displayed in different structural contexts on the surfaces of the pathogenic organisms, Streptococcus pneumoniae, Ascaris suum and Trichinella spiralis as well as Proteus morganii; 2) by testing the ability of mutant antibodies to transmit antigen-induced signals to transfected B lymphoma cells, and 3) by examining apoptotic GC B-cells for mutations in the VH1 gene of T15 shown to be harmful in vitro. These studies bear on B-cell wastage and homeostasis and the causes of apoptosis in germinal centers where recent evidence has suggested some lymphoid tumors such as Hodgkin's disease may originate.